1. Field of the Invention
The present invention relates to an information processing apparatus, an information processing method, a recording medium and a program. More particularly, the present invention relates to an information-processing apparatus suitable for a process to edit video data compressed by adoption of a bi-directional inter-frame prediction technique, an information processing method adopted by the information-processing apparatus, a program for implementing the information processing method and a recording medium used for recording the program.
2. Description of the Related Art
In accordance with image compression methods represented by the MPEG (Moving Picture Coding Experts Group/Moving Picture Experts Group) technique, a video signal is subjected to a compression/coding process based on an inter-frame prediction technique in order to realize a high compression efficiency. If a process to edit an image is taken into consideration, however, an image compressed by adoption of an inter-frame prediction technique is an image represented by a signal compressed by adoption of the inter-frame prediction technique. Thus, video materials cannot be linked to each other by using the signal compressed as it is. As a result, in a system taking edition of video materials into consideration in advance, in general, the inter-frame prediction technique is not adopted. Instead, a coding process based on only an intra-image compression technique is carried out.
In a process to handle a video signal having a high degree of precision and conveying a lot of information as is the case with for example an HD (High Definition) signal, however, a coding process based on only an intra-image compression technique will result in a low compression efficiency. Thus, in order to transmit and or store data of a large amount as data compressed at a low compression efficiency, it is undesirably necessary to use an expensive system, which is at least capable of transmitting data at a high transmission speed, provided with a storage unit having a large storage capacity and capable of carrying processing at a high processing speed. That is to say, in order to handle a video signal having a high degree of precision and conveying a lot of information by making use of a low-cost system, it is necessary to raise the compression efficiency by adoption of the inter-frame prediction technique.
Related technology in the past is the one which was adopted in a process to edit an MPEG stream. In accordance with the related technology, pictures in the neighborhood of an edit point also referred to as a splicing point were decoded once to generate decompressed video signals. Then, decompressed video signals obtained as a result of the decoding process were linked to each other at the edit points. Finally, a signal obtained as a result of linking at the edit points was again encoded. (See PCT Patent Publication No. WO99/05864, hereinafter referred to as Patent Document 1)
In the MPEG technology, the compression/encoding method adopting the bi-directional inter-frame prediction technique is referred to as a long GOP (Group of Picture) method since a video stream subjected to the compression/encoding process based on the bi-directional inter-frame prediction technique is converted into a sequence of I pictures, P pictures and B pictures.
An I picture is a picture obtained as a result of an intra-frame encoding process. Thus, an I picture can be encoded independently of other screens (frames or pictures). That is to say, an I picture can be decoded on the basis of only information conveyed by the picture itself. A P picture is a picture obtained as a result of an inter-frame forward-directional prediction encoding process. To be more specific, a P picture is obtained as a result of a forward-directional prediction encoding process as a picture expressed in terms of differences from a preceding frame. A B picture is a picture obtained as a result of an inter-frame bi-directional prediction encoding process.
The amount of data contained in a P and B picture is small in comparison with an I picture. Thus, for a long GOP of a stream or a large number of pictures composing a long GOP of a stream, the compression efficiency of the pictures of the stream cannot be increased. For this reason, the inter-frame prediction technique is suitable for utilization of digital broadcasting and a DVD (Digital Versatile Disk) video. If the GDP is excessively long, however, the editing control at frame precision becomes difficult to execute, particularly, in an editing work for a business application.
By referring to FIG. 1, the following description explains a process to link two pieces of video data, which has been compressed by adoption of the long GOP method, at predetermined edit points.
First of all, a portion included in edit-object compressed data 1 as a portion in the vicinity of an edit point of the edit-object compressed data 1 and a portion included in edit-object compressed data 2 as a portion in the vicinity of at an edit point of the edit-object compressed data 2 are subjected to a partial decoding process to produce a partial decompressed video signal 1 and a partial decompressed video signal 2. Then, the partial decompressed video signal 1 and the partial decompressed video signal 2 are linked to each other at the edit points in order to generate an edited signal. If necessary, an effect process is carried out in the vicinity of the edit points and, subsequently, a re-encoding process is performed on the edited signal to generate compressed and encoded video data. Then, the compressed and encoded video data obtained as a result of the re-encoding process is linked to compressed and encoded video data not subjected to the partial decoding process and the re-encoding process. The compressed and encoded video data not subjected to the partial decoding process and the re-encoding process is video data other than the portion included in the edit-object compressed data 1 as a portion in the vicinity of the edit point of the edit-object compressed data 1 and other than the portion included in the edit-object compressed data 2 as a portion in the vicinity of the edit point of the edit-object compressed data 2.
By virtue of the method explained above by referring to FIG. 1, it is possible to confine picture deteriorations caused by the re-encoding process to portions in the vicinity of the edit points and possible to substantially shorten the editing time in comparison with the method whereby, after compressed video data to be edited is all subjected to a decoding process, video signals obtained as a result of the decoding process are linked to each other at edit points to produce an edited signal, and the edited signal is again subjected to a re-encoding process to generate edited compressed video data.